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Title: Sol-gel processing and phase characterization of Al{sub 2}O{sub 3} and Al{sub 2}O{sub 3}/SiC nanocomposite powders

Abstract

Monolithic Al{sub 2}O{sub 3} and Al{sub 2}O{sub 3}/SiC nanocomposite powders were prepared by sol-gel processing. The process involved the precipitation of Al(NO{sub 3}){sub 3}.9H{sub 2}O with NH{sub 4}OH in excess water to form boehmite (AlOOH). XRD indicates that the subsequent thermal reaction proceeds by the phase transformation sequence AlOOH, {gamma}-, {delta}-, {theta}-, to {alpha}-Al{sub 2}O{sub 3}. The {sup 27}Al NMR spectra indicate a gradual increase in the proportion of Al in the tetrahedral sites of the {gamma}-, {delta}- and {theta}-Al{sub 2}O{sub 3} formed at increasing calcination temperatures. Complete transformation to octahedral Al ({alpha}-Al{sub 2}O{sub 3}) is marked by the abrupt disappearance of tetrahedral Al. Al{sub 2}O{sub 3}/SiC nanocomposite powders were prepared by adding {alpha}-SiC powder to the boehmite precursor at the precipitation stage. Upon heating, the {sup 29}Si NMR spectra of the Al{sub 2}O{sub 3}/SiC powders reveal {alpha}-SiC, Al{sub 2}O{sub 3}.xSiO{sub 2} and SiO{sub 2} phases. Stable {alpha}-Al{sub 2}O{sub 3} and {alpha}-Al{sub 2}O{sub 3}/SiC nanocomposite powders are formed at 1200 and 1300 deg. C, respectively. It appears likely that the presence of SiC modifies the thermal behaviour of the Al{sub 2}O{sub 3} in the nanocomposites by stabilising the Al{sub 2}O{sub 3} phases with concomitant oxidation of SiO{sub 2}.

Authors:
 [1];  [2]
  1. Department of Physics, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand). E-mail: sukanda@chiangmai.ac.th
  2. School of Chemical and Physical Sciences, Victoria University of Wellington, P.O. Box 600, Wellington (New Zealand)
Publication Date:
OSTI Identifier:
20891662
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Research Bulletin; Journal Volume: 41; Journal Issue: 4; Other Information: DOI: 10.1016/j.materresbull.2005.10.014; PII: S0025-5408(05)00388-0; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM OXIDES; AMMONIUM HYDROXIDES; CALCINATION; CALORIMETRY; CERAMICS; COMPOSITE MATERIALS; HEATING; NANOSTRUCTURES; NITRATES; NITROGEN OXIDES; NMR SPECTRA; NUCLEAR MAGNETIC RESONANCE; POWDERS; SILICA; SILICON OXIDES; SOL-GEL PROCESS; X-RAY DIFFRACTION

Citation Formats

Jiansirisomboon, Sukanda, and MacKenzie, Kenneth J.D. Sol-gel processing and phase characterization of Al{sub 2}O{sub 3} and Al{sub 2}O{sub 3}/SiC nanocomposite powders. United States: N. p., 2006. Web. doi:10.1016/j.materresbull.2005.10.014.
Jiansirisomboon, Sukanda, & MacKenzie, Kenneth J.D. Sol-gel processing and phase characterization of Al{sub 2}O{sub 3} and Al{sub 2}O{sub 3}/SiC nanocomposite powders. United States. doi:10.1016/j.materresbull.2005.10.014.
Jiansirisomboon, Sukanda, and MacKenzie, Kenneth J.D. Thu . "Sol-gel processing and phase characterization of Al{sub 2}O{sub 3} and Al{sub 2}O{sub 3}/SiC nanocomposite powders". United States. doi:10.1016/j.materresbull.2005.10.014.
@article{osti_20891662,
title = {Sol-gel processing and phase characterization of Al{sub 2}O{sub 3} and Al{sub 2}O{sub 3}/SiC nanocomposite powders},
author = {Jiansirisomboon, Sukanda and MacKenzie, Kenneth J.D.},
abstractNote = {Monolithic Al{sub 2}O{sub 3} and Al{sub 2}O{sub 3}/SiC nanocomposite powders were prepared by sol-gel processing. The process involved the precipitation of Al(NO{sub 3}){sub 3}.9H{sub 2}O with NH{sub 4}OH in excess water to form boehmite (AlOOH). XRD indicates that the subsequent thermal reaction proceeds by the phase transformation sequence AlOOH, {gamma}-, {delta}-, {theta}-, to {alpha}-Al{sub 2}O{sub 3}. The {sup 27}Al NMR spectra indicate a gradual increase in the proportion of Al in the tetrahedral sites of the {gamma}-, {delta}- and {theta}-Al{sub 2}O{sub 3} formed at increasing calcination temperatures. Complete transformation to octahedral Al ({alpha}-Al{sub 2}O{sub 3}) is marked by the abrupt disappearance of tetrahedral Al. Al{sub 2}O{sub 3}/SiC nanocomposite powders were prepared by adding {alpha}-SiC powder to the boehmite precursor at the precipitation stage. Upon heating, the {sup 29}Si NMR spectra of the Al{sub 2}O{sub 3}/SiC powders reveal {alpha}-SiC, Al{sub 2}O{sub 3}.xSiO{sub 2} and SiO{sub 2} phases. Stable {alpha}-Al{sub 2}O{sub 3} and {alpha}-Al{sub 2}O{sub 3}/SiC nanocomposite powders are formed at 1200 and 1300 deg. C, respectively. It appears likely that the presence of SiC modifies the thermal behaviour of the Al{sub 2}O{sub 3} in the nanocomposites by stabilising the Al{sub 2}O{sub 3} phases with concomitant oxidation of SiO{sub 2}.},
doi = {10.1016/j.materresbull.2005.10.014},
journal = {Materials Research Bulletin},
number = 4,
volume = 41,
place = {United States},
year = {Thu Apr 13 00:00:00 EDT 2006},
month = {Thu Apr 13 00:00:00 EDT 2006}
}
  • Yttria-stabilized cubic zirconia powders and coatings produced by the sol-gel method have been investigated by Perturbed Angular Correlation Spectroscopy (PAC). Results indicate that the metastable cubic phase is retained during heating and cooling cycles. The hyperfine interaction that describes this cubic phase, once crystallized, exhibits two components in a constant ratio of 4:1. The components represent different vacancy configurations. For the fast movement of oxygen vacancies starting at 750{degree}C, which is reflected by the damping of the hyperfine pattern, an activation energy of 0.96 eV was determined. {copyright} {ital 1997 Materials Research Society.}
  • Powders and coatings of zirconia doped with 2.5 mole {percent} yttria have been produced via the sol-gel route. The phase structure and subsequent thermal evolution in heating and cooling cycles have been investigated using mainly perturbed angular correlations spectroscopy. Thermal analyses and XRD as a function of temperature have also been performed to obtain complementary information. Upon heating, the amorphous gels crystallized into the tetragonal structure and showed the same hyperfine pattern and thermal behavior as observed in tetragonal zorconia obtained by the ceramic route: the two configurations vacancies around zirconium ions denoted as t{sub 1} and t{sub 2} formsmore » and their mutual t{sub 1}{r_arrow}t{sub 2} transformation. While the powder sample exhibited an incipient thermal instability above 1000{degree}C and underwent completely the t{sub 2} form to m{endash}ZrO{sub 2} transition during subsequent, gradual cooling below 500{degree}C, the coating retained the tetragonal phase within the whole temperature range investigated. Hyperfine results suggest that the tetragonal phase stabilization is favored by the highly defective nature of the t{sub 1} form and consequently hardened by the availability of oxygen. The PAC derived activation energy for the fast diffusion of the oxygen vacancies inherent to the t{sub 2} form was determined as 0.54{plus_minus}0.14eV. {copyright} {ital 1997 Materials Research Society.}« less
  • The high {ital T}{sub {ital c}} superconducting oxide YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital d}} has been fabricated by a simple colloidal sol-gel precursor technique based on citrate complexes uniformly dispersed into ethyleneglycol and water. The present method permits easier fabrication of highly pure and homogeneous superconducting materials when compared with other more elaborate preparation procedures based on solution techniques as it eliminates many steps such as centrifugation, filtration, and {ital p}H control. The purity of the final product was estimated to be {gt}99.5% based on the combined results of x-ray diffraction and Raman scattering analyses. The composition of the sample wasmore » determined to be Y{sub 1.00}Ba{sub 1.98}Cu{sub 3.05}O{sub 6.85} by inductively coupled plasma spectroscopy and idiometry. The sol-gel process produced homogeneous materials with particle sizes smaller than {similar to}3 {mu}m. The superconducting transition determined with resistivity measurements was shown to be sharp with a transition width narrower than 1 K. The magnetic susceptibility measurements exhibited sharp superconducting transitions without any indication of two-phase character or impurity phases. The material fabricated by this method showed improved properties compared to those prepared by the usual dry powder-mix (so-called solid-state reaction) technique.« less
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